The present invention relates to humidity sensor structures and to improved fabrication techniques for manufacturing such structures.
Commercially acceptable absolute humidity sensors have been known for some time. A particularly successful sensor is described and claimed in Goodman et al. U.S. Pat. No. 3,523,244, owned by the assignee of the present invention and incorporated herein by reference. The structure taught in that patent consists of an aluminum foil which is anodized to form a porous Al.sub.2 O.sub.3 layer on one surface of the foil. A thin, moisture permeable gold layer is then deposited over the porous Al.sub.2 O.sub.3 to produce, essentially, a parallel plate impedance that is sensitive to the water vapor that can easily penetrate the thin gold layer. The overlying gold layer and the underlying aluminum foil form the parallel plates of the impedance. Electrical contact to the thin gold film can be made in a number of ways, one of which utilizes a spring-loaded metal finger that makes mechanical contact with the gold film.
Despite the substantial success of the absolute humidity sensor described in U.S. Pat. No. 3,523,244, its design has dictated stringent fabrication requirements. Thus, it is a principal object of the present invention to provide an improved absolute humidity sensor design which is conducive to relatively inexpensive fabrication and accurate measurement. Another object is the provision of fabrication methods which will yield accurate humidity sensors efficiently and inexpensively.